This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As our telescopes have improved and we've been able to peer farther back in time, we've begun finding more fascinating features of the universe. But one thing we haven't found for sure is Population III (Pop III) stars.
These were the earliest stars in the universe, formed completely from pristine hydrogen and helium, with no "metals" (i.e., elements heavier than those two) polluting their processes. They are also theorized to be extremely massive and to "die with passion," as Bill Wurtz once put it in a famous YouTube video. A new paper, available on the arXiv preprint server by Tae Bong Jeon of the Cosmic Frontier Center at the University of Texas at Austin, looks at how massive those starbursts could be and whether the James Webb Space Telescope could detect one.
So far, JWST has found hints of them—and at much later periods than would have been expected based on theoretical models from before the telescope was launched. Some galaxies near the end of the Epoch of Reionization have features that appear to come from these pristine starbursts, but hundreds of millions of years later than predicted. For that to happen, two existential traps must be avoided.
First, the hydrogen and helium gas clouds that form these stars can't collapse too early. Second, they must avoid being "contaminated" by metals from neighboring supernovae. Let's first look at how to delay a gas cloud's collapse.
In the early universe, primordial gas clouds could collapse under their own gravity only if they could cool down. Typically, once they got dense enough, they would simply heat up, causing them to expand again. Crucially, the only "coolant" they had was molecular hydrogen (H2).
This critical molecule was a key feature in the formation of the first Pop III stars, as it allowed dark matter to pull enough gas close enough together for fusion to start. In later phases of the universe, however, molecular hydrogen was more abundant, so, at least in theory, Pop III stars would form more readily and, given their short life spans, burn out well before the periods in which JWST is seeing them. One potential solution to this puzzle is to reduce the amount of molecular hydrogen available as a coolant near those gas clouds.
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